For ease of manufacture and cost effectiveness, an electronic system is generally manufactured on several separate printed circuit boards. These separate printed circuit boards are then connected to one another by electrical connectors. Typically, one printed circuit board serves as a backplane. Other printed circuit boards, often called daughter boards or daughter cards, are then connected to the backplane by electrical connectors as part of the electronic system.
To meet the demand for electronic systems that are more compact, faster, and more complex, increasingly more circuits are placed within a given area of each printed circuit board, and those circuits operate at increasingly higher frequencies. Correspondingly, the electrical connectors between the printed circuit boards have to pass data at increasingly higher rates. For fast data processing, current electronic systems require faster data transmission between their component printed circuit boards.
However, as a result of increasing signal frequencies, the connectors encounter more electrical noise. The electrical noise often manifests itself as signal reflections, crosstalk, electromagnetic radiation, or other similar forms of electrical noise. Signal reflection occurs when a portion of a signal being transmitted is reflected back to the signal source instead of being transmitted to the signal destination. Signal reflections are caused by signal path imperfections that give rise to impedance mismatching. Also, changes in the signal path characteristics, particularly abrupt changes, can cause signals to be reflected.
Crosstalk is electromagnetic coupling of one signal path with another signal path. The coupling results in one signal affecting another nearby signal. To reduce electrical noise in the form of crosstalk, signal paths are arranged so that the signal paths are spaced farther apart from each other and nearer to a shield plate which is generally the ground plate, as described in U.S. Patent Application Pub. No. 2004/0264153 to Payne et al., entitled “Printed Circuit Board for High Speed, High Density Electrical Connector with Improved Cross-Talk Minimization, Attenuation and Impedance Mismatch Characteristics,” which is incorporated by reference herein in its entirety. Therefore, the signal paths tend to couple electromagnetically more with the shield plate and less with each other. For a particular level of crosstalk, the signal paths can be placed closer to each other as long as sufficient electromagnetic coupling to the shield plate or a ground conductor is maintained.
Also, in a region where the signal path electrically connects to another circuit, manufacturing costs are relatively higher since the signal path must be formed and shaped to provide an acceptable electrical connection that is mechanically durable. Such connections are typically more difficult to manufacture because a more complicated shape is required and therefore is more costly to form. The connections also need electromagnetic coupling to the shield plate or to ground conductors to minimize crosstalk.
One approach to lower costs and provide shielding between adjacent connections is to use plastic containing conductive materials, such as the connector described in U.S. Patent Application Pub. No. 2007/0042639 to Manter et al., entitled “Connector with Improved Shielding in Mating Contact Region,” which is incorporated by reference herein in its entirety. However, the use of plastic containing conductive materials between signal paths does not provide the stiffness, the shielding, or the lower relative manufacturing cost of using a metal shield.
Therefore, there is a need in the art for a high speed, high density electrical connector design that minimizes crosstalk, provides increased conductive metal content around the contact region, and lowers manufacturing costs.